Fresh tissues contain viable antigen presenting cells which can immunize the recipient against donor tissue antigens and cause graft rejection. This presents problems in matching donors and recipients and is a barrier against interspecies transplantation. Donor antigen presenting cells, for example dendritic cells of the transplanted tissue, present foreign antigens to recipient T cells. A resulting immune response can result in the rejection of the foreign, that is, donor or transplanted, tissue.
In some transplantation procedures, such as those transplanting bone, living cells of the transplanted material are not necessary. The intercellular matrix support is the important component. Bone tissue has been freeze dried, causing necrosis of the cells of the bone matrix. When freeze dried bone tissue is transplanted it is immunoneutral.
There is also particular concern regarding the immunological effects of the antigen-presenting leukocytes that contaminate transfused blood products. In patients receiving subsequent blood transfusions, this immunization can result in febrile transfusion reactions or, in the case of platelet transfusions, the destruction of the platelets.
In response to this problem there is an increasing trend toward the routine filtration of red blood cell and platelet products in order to remove leukocytes. The filters add considerable cost to the blood products, and in addition present their own disposal problem as biohazardous waste. Moreover, even the best filters leave 10.sup.6 or so leukocytes in the cell suspension.
There is also significant loss of blood product during the filtration procedure. The loss of platelets due to filtration is particularly severe, averaging approximately 25% of the platelet product.
Filtration also does not solve yet another problem associated with leukocytes contaminating blood products, that of transmission of viral diseases in which the viral particles, such as cytomegalovirus, reside within leukocytes. Since filtration leaves approximately 10.sup.6 leukocytes in suspension, viral particles within these cells are capable of infecting a transfusion recipient.
Heating is another method which has been used for reducing immunogenicity in blood products. A blood product heated to 39.degree. to 40.degree. C. for thirty to sixty minutes demonstrates a reduced immunogenicity, but the mechanisms responsible for this reduction have not been described in the literature.
Exposure to short wavelength light, either UV-B, for platelet products, or gamma radiation, for blood cell products, has been found to reduce immunogenicity. It is difficult to control the exposure throughout the sample, as intensity of the radiation decreases with distance from the source, and the intensity decreases as the radiation is absorbed as it traverses the sample. This exposure also results in the formation of free radicals which can damage extracellular components as well as cells in the sample.
A procedure whereby both the immunoactivity and the threat of infection could be substantially reduced or eliminated would increase the safety of transplanting tissues including the transfusion of blood products.